It relates particularly to electrochemical cells having an alkaline electrolyte and in which at least one of the electrodes comprises a porous metal support filled with active material. The porous support has a matrix structure comparable to that of a sponge with the cells thereof being interconnected in a three-dimensional network: it is designated herein by the term "foam".
Before being filled with active material, the porosity of the foam is greater than 90%. After being filled, the electrode is compressed to specified thickness, thereby facilitating assembly and ensuring that the cell operates properly.
The cells concerned may include electrodes that are planar or that are spiral-wound.
Such an electrode is connected to a terminal of the cell by joining a metal connection tab thereto.
To implement such an operation, transposing technologies that are well-known for other types of electrodes would give rise to one of the four following methods:
welding a metal part or an unfilled foam connection tab to the foam of the support in a weld zone which is generally not filled with active material; PA1 cutting out the foam of the support (optionally filled with active material) so as to provide a connection tab; PA1 riveting or stapling a metal part onto the foam where it is filled with active material; or PA1 compressing a connection tab made of unfilled foam onto the support foam where it is filled with active material. PA1 a negligible reduction in the active surface area of the electrode since the active material of the electrode can function level with the connection tab; PA1 the geometrical shape of the connection tab is simple and it is simple to install during compression of the support without requiring an extra operational stage; and PA1 electrodes can be made that are suitable for welding on their edges, thereby making it possible to obtain electrodes whose power characteristics are greater than those of electrodes having connection "tongues", and which are interchangeable with prior art electrodes using conventional supports.
The first method suffers from the drawback of welding having mediocre reliability when applied to thin components. An additional operation is often required to prepare the surface of the electrode for welding.
The second method gives rise to a component which is fragile and which often breaks during the subsequent operations applied thereto. In addition, cutting out a connection tab from the foam engages a cost penalty: foam is lost, possibly together with high value active material.
The third method using rivets or staples stiffens the support and as a result it becomes significantly less suitable for the bending required in spiral-wound electrodes.
The foam connection tab obtained using the fourth method is expensive and fragile.
These various methods also suffer from the drawback of reducing the active surface area of the electrodes.
An object of the present invention is to implement a joining method that does not require an additional operational stage, and that reduces the active surface area of the electrode by a negligible amount only.